1. Field of the Invention
The invention relates to a spacer retaining structure for locking connecting terminals within a housing, and more particularly to a spacer retaining structure for retaining a spacer in a hollow portion arranged within the housing.
2. Related Art
Various types of spacer retaining structures have theretofore been known. For example, Unexamined Japanese Patent Publication No. Hei. 5-144499 discloses the following spacer retaining structure.
The conventional spacer retaining structure 51 shown in FIG. 6 has a housing 2 and a terminal locking spacer 60. The housing 2 has not only a plurality of axially extending terminal accommodating chambers 6 arranged therein, but also a hollow portion 5 formed in the middle portion of one of outer peripheral walls 3, i.e., a top wall 3a so as to pass through the housing 2 vertically while traversing partition walls 4. The spacer 60 has not only openings 8 that correspond to the plurality of terminal accommodating chambers 6 but also lock portions 9 that retain connecting terminals 7 at the openings 8, and moves from a temporarily retained position to a regularly retained position while inserted from the hollow portion 5.
Each of vertical wall portions 11 that constitute the spacer 60 has not only temporarily retaining projections 12 disposed on the front end face side thereof, but also flexible members 65 having regularly retaining projections 14 formed through slits 63 on the rear end face side thereof, each flexible member 65 being supported at both ends thereof. Further, the housing 2 has temporarily retaining portions 16 and regularly retaining portions 17 arranged. Each temporarily retaining portion 16 is engageable with the corresponding temporarily retaining projection 12 when the openings 8 are inserted to positions substantially coinciding with the terminal accommodating chambers 6. Further, each regularly retaining portion 17 is engageable with the corresponding regularly retaining projection 14 when a lock portion 9 engages with a corresponding retaining hole 25 of a connecting terminal 7 to reach a regularly retained position from the aforementioned retained position, the regularly retained position being such a position as to prevent the terminal from being released from the rear.
It may be noted that the flexible members 65 are arranged on the side walls 61a serving as the vertical wall portions 61 positioned on both ends of the spacer 60, but also the slits 63 are arranged so as to pass through slit openings 63a formed in a top wall 68. However, one end of each flexible member 65 is coupled and fixed to the corresponding side wall 61a at a coupling portion 68a of the top wall 68, so that the flexible member 65 is fixed at both ends thereof. Further, each regularly retaining projection 14 is arranged almost in the middle of the rear end face of the corresponding flexible member 65.
Further, a flexible lock arm 24 engageable with a retaining hole 25 of the connecting terminal 7 is arranged on an inner peripheral wall confronting a bottom wall 21 in the front of each of the plurality of terminal accommodating chambers 6 independently of the lock portion 9.
Further, in order to facilitate the retaining operation, slopes 12a, 16a are arranged on the lower surface of each temporarily retaining projection 12 and the upper surface of each temporarily retaining portion 16. Further, slopes 14a, 17a are arranged on the upper and lower surfaces of each regularly retaining projection 14 and the upper surface of each regularly retaining portion 17.
In the thus constructed conventional spacer retaining structure 51, first, the spacer 60 is inserted from above the hollow portion 5 of the housing 2, and when the spacer 60 has reached the temporarily retaining position, the temporarily retaining projections 12 are retained by the temporarily retaining portions 16. At this instance, the openings 8 of the spacer 60 substantially coincide with the terminal accommodating chambers 6. Then, when the connecting terminal 7 having a wire 26 caulked at the rear portion thereof is inserted from the rear end of a terminal accommodating chamber 6, the retaining hole 25 is retained with the flexible lock arm 24, so that the connecting terminal 7 can be prevented from being released from the rear.
Then, when the spacer 60 is pushed further downward, not only the regularly retaining projections 14 are retained by the regularly retaining portions 17, so that the spacer 60 is retained in the regularly retained position, but also the connecting terminal 7 is retained by the corresponding lock portion 9, so that the connecting terminal 7 can be prevented from being released from the rear doubly.
However, in the aforementioned conventional spacer retaining structure 51, each flexible member 65 is fixedly supported at both ends thereof as shown in FIG. 9. Therefore, in order to set the amount of flexion at a regular retaining projection 14 to such a predetermined value .delta..sub.22 as to be retained by the corresponding regularly retaining portion 17, the length l.sub.2 of the flexible member 65, i.e., the length of the slit 63 must be made larger than that of a cantilevered flexible member as will be described later using theoretical equations. Therefore, the height L.sub.2 of the spacer 60 becomes larger, which in turn imposes the problem of increasing also the size of the housing 2.
Further, when the length of the flexible member 65 is reduced, the maximum tensile stress caused within the flexible member 65 is increased as will also be described later using theoretical equations. Therefore, when the spacer 60 is attached to and detached from the hollow portion 5 of the housing 2 frequently, the flexible members 65 become so weak as to be plastically deformed or even broken in some cases.
Then, differences in mechanical performance between the aforementioned cantilevered flexible member 75 and the flexible member 65 supported at both ends will be described with reference to FIGS. 7 to 9. Assuming that the length of the cantilevered flexible member 75 shown in FIGS. 7 and 8 is l.sub.1 ; the pushing force to be applied to the corresponding regularly retaining projection 14 that serves as an acting point is W.sub.1 ; the flexion at the acting point is .delta..sub.1, the maximum bending moment caused within the flexible member 75 is M.sub.1 max ; the second moment of inertia obtained by the cross section of a beam is I; and the Young's modulus of a material is E, then the flexion .delta..sub.1 is given as follows. EQU .delta..sub.1 =W.sub.1 .multidot.(l.sub.1).sup.3 /3EI (1) EQU M.sub.1 max .varies.W.sub.1 .multidot.l.sub.1 (2)
Similarly, assuming that the span of the flexible member 65 as a beam supported at both ends shown in FIGS. 6 and 9 is l.sub.2 ; the pushing force to be applied to the corresponding regularly retaining projection 14 that serves as an acting point is W.sub.2 ; the flexion at the acting point is .delta..sub.2, the maximum bending moment caused within the flexible member 65 is M.sub.2 max ; the second moment of inertia obtained by the cross section of a beam is I; and the Young's modulus of a material is E, then EQU .delta..sub.2 .varies.W.sub.2 .multidot.(l.sub.2).sup.3 /192EI (3) EQU M.sub.2 max =W.sub.2 .multidot.l.sub.2 /8 (4)
Here, if the requirement for causing the flexible member 65 supported at both ends thereof and the cantilevered flexible member 75 to apply the pushing forces serving as the same holding force with the same flexion so that the regular retaining projections 14 respectively arranged on the flexible members 65, 75 can ride over the corresponding regular retaining portions 17 and so that the regularly retaining projections 14 can be held strongly is a requirement for satisfying .delta..sub.1 =.delta..sub.2 and W.sub.1 =W.sub.2. Therefore, this requirement can be expressed as follows using equations (1) and (3). EQU W.sub.1 .multidot.(l.sub.1).sup.3 /3EI=W.sub.2 .multidot.(l.sub.2).sup.3 /192EI (5)
When equation (5) is simplified using the above conditions, EQU l.sub.2 =4.multidot.(l.sub.1) (6)
According to equation (6), the span l.sub.2 of the flexible member 65 supported at both ends must be four times the arm length l.sub.1 of the cantilevered member 75. Therefore, if the flexible member 65 is of the type that is fixedly supported at both ends, the height of the spacer 60 and the housing 2 is increased, and this in turn imposes the problem that the size of the spacer 60 and the housing 2 is increased.
Then, the maximum tensile stresses caused within the flexible members 65, 75 when the flexion .delta..sub.1 is equal to the flexion .delta..sub.2 are compared by setting the lengths of the flexible members 65, 75 to the same value, i.e., l.sub.1 =l.sub.2. In this case, what is required to do is to compare the maximum bending moments M.sub.1 max and M.sub.2 max since both flexible members 65, 75 have the same cross section and are made of the same material. When simplified using this requirement, equation (5) becomes as follows. EQU W.sub.2 =64.multidot.W.sub.1 (7)
Further, if the quotient obtained by dividing equation (4) by equation (2) is substituted into equation (7), the following equation can be given. EQU M.sub.2 max =8.multidot.M.sub.1 max (8)
This equation (8) indicates that the maximum tensile stress caused within the flexible member 65 of the type that is fixedly supported at both ends is eight times the maximum tensile stress caused within the cantilevered flexible member 75 under the aforementioned requirement.
Thus, if the flexible member 65 is of the type that is fixedly supported at both ends, the maximum tensile stress caused is greater than that of the cantilevered flexible member 75. Therefore, when the spacer 60 is attached to and detached from the housing 2 frequently, imposed is the problem that the flexible member 65 becomes so weak as to be plastically deformed or even broken in some cases.
Further, to have the flexible member 65 replaced with the cantilevered flexible member 75 as shown in FIG. 7 in order to overcome the aforementioned problem, not only the coupled portion 68a of the top wall 68 shown in FIG. 6 must be cut away and removed, but also a cut groove 70 must be formed in order to separate the flexible member 65 from the top wall 68 and an intermediate partition wall 69. Otherwise, the function as the cantilevered flexible member cannot be performed. Therefore, another problem that the molds to be used become complicated, which in turn elevates the cost of manufacture.